There is increasing interest in the electronic arts in devices that are suitable for surface mounting, that is, devices whose leads are coplanar and designed to be soldered to the surface of planar metal pads on a circuit board or the like rather than penetrating through holes in the circuit board. A number of surface mount package designs, as for example types SOT-23, SOT-143 and SO-8, are already in widespread use. Plastic Leaded Chip Carriers (PLCC's) are another example of a well known surface mount package design. The electrical leads of these various surface mount package designs are generally of the "gull-wing" or "J-form" type. These lead configurations are well known in the art.
Most of the surface mount packages that have so far come into use have been intended for lower frequency analog operation or for complex digital IC's having large numbers of leads. While these packages are useful, they are not well adapted for use in connection with high frequency devices or IC's, that is devices operating in the range of above 25 megahertz, more particularly above about 100 megahertz and especially for operation above about 200-500 megahertz. It is not unusual to have such high frequency devices operating at frequencies as high as 25 gigahertz. Among the problems encountered in attempting to use prior art devices and/or device packages at high frequencies are, excessive lead length, significant parasitic inductance and capacitance, and excessive thermal impedance. These problems become more severe as the desired operating frequency increases.
For example, semiconductor device operation at such high frequencies generally requires very high current densities. As a result, the internal power dissipation of the device is also quite high, for example, in the range of one to three Watts or more. Unless great care is taken to provide a package configuration with low thermal impedance, junction temperatures will be high and operating life will be shortened. In addition, the lead length and impedance must be minimized, especially in the common (electric reference) leads since parasitic impedance in such leads is degenerative. For these and other reasons well known in the art, the design of devices and/or device packages for operation at such high frequencies must be different than the usual design practice in connection with lower frequency devices and/or IC's.
The device packages generally used for such high frequency range are often made from expensive materials such as ceramic, glass and/or metal, and have a multiplicity of metal layers or internal piece parts or both. For these and other reasons well known in the art most prior art high frequency packages are expensive. There is an ongoing need for improved means and methods for high frequency device packages and devices, especially packages and devices that use low cost materials and methods, that have low thermal and parasitic impedance, that are suitable for surface mounting, and that handle substantially amounts of power, i.e., .gtoreq.1 Watt, especially .gtoreq.3 watts.